Magnetic recording apparatus having circuits with differing tunnel valve sensors and about the same resistance

ABSTRACT

An apparatus, according to one embodiment, includes a plurality of first circuits, each first circuit comprising a pair of terminals coupled to a first read transducer and a first parallel circuit. A terminal resistance of each first circuit is less than the resistance of the first read transducer thereof. A second circuit has a pair of terminals that are coupled to a second read transducer having a tunnel valve structure. An area of a tunnel barrier portion of the second read transducer is larger than an area of a tunnel barrier portion of each of the first read transducers. A resistivity of a tunnel barrier of each of the first read transducers is about the same as a resistivity of a tunnel barrier layer of the second read transducer. The terminal resistance of each first circuit is less than about five times a terminal resistance of the second circuit.

BACKGROUND

The present invention relates to data storage systems, and moreparticularly, this invention relates to magnetic recording modules, inparticular, magnetic recording modules having tunnel valve sensorcircuits with similar resistances, but two or more of the tunnel valvesensors in the circuits have dissimilar tunnel barrier areas and thusdifferent resistance values thereacross.

In magnetic storage systems, magnetic transducers read data from andwrite data onto magnetic recording media. Data is written on themagnetic recording media by moving a magnetic recording transducer to aposition over the media where the data is to be stored. The magneticrecording transducer then generates a magnetic field, which encodes thedata into the magnetic media. Data is read from the media by similarlypositioning the magnetic read transducer and then sensing the magneticfield of the magnetic media. Read and write operations may beindependently synchronized with the movement of the media to ensure thatthe data can be read from and written to the desired location on themedia.

An important and continuing goal in the data storage industry is that ofincreasing the density of data stored on a medium. For tape storagesystems, that goal has led to increasing the track and linear bitdensity on recording tape, and decreasing the thickness of the magnetictape medium. However, the development of small footprint, higherperformance tape drive systems has created various problems in thedesign of a tape head assembly for use in such systems.

In a tape drive system, the drive moves the magnetic tape over thesurface of the tape head at high speed. Usually the tape head isdesigned to minimize the spacing between the head and the tape. Thespacing between the magnetic head and the magnetic tape is crucial andso goals in these systems are to have the recording gaps of thetransducers, which are the source of the magnetic recording flux in nearcontact with the tape to effect writing sharp transitions, and to havethe read elements in near contact with the tape to provide effectivecoupling of the magnetic field from the tape to the read elements.

SUMMARY

An apparatus, according to one embodiment, includes a plurality of firstcircuits, each first circuit comprising a pair of terminals coupled to afirst read transducer and a first parallel circuit, each first readtransducer having a tunnel valve structure having a resistance. Aterminal resistance of each first circuit is less than the resistance ofthe first read transducer thereof. A second circuit has a pair ofterminals that are coupled to a second read transducer having a tunnelvalve structure. An area of a tunnel barrier portion of the second readtransducer along a plane of deposition thereof is larger than an area ofa tunnel barrier portion of each of the first read transducers along aplane of deposition thereof. A resistivity of a tunnel barrier of eachof the first read transducers is about the same as a resistivity of atunnel barrier layer of the second read transducer. The terminalresistance of each first circuit is less than about five times aterminal resistance of the second circuit.

An apparatus according to another embodiment includes a module having anarray of first read transducers and a second read transducer, the firstand second read transducers each having a tunnel valve structure. Anarea of a tunnel barrier portion of the second read transducer along aplane of deposition thereof is larger than an area of a tunnel barrierportion of each of the first read transducers along a plane ofdeposition thereof. A parallel circuit is coupled to each of the firstread transducers. A cable couples the first and second read transducersto a controller, thereby forming a plurality of circuits extending fromthe controller, each circuit corresponding to one of the readtransducers. A terminal resistance of each circuit corresponding to thefirst read transducers is less than about five times a terminalresistance of the circuit corresponding to the second read transducer.

Other aspects and embodiments of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of a simplified tape drive systemaccording to one embodiment.

FIG. 1B is a schematic diagram of a tape cartridge according to oneembodiment.

FIG. 2A illustrates a side view of a flat-lapped, bi-directional,two-module magnetic tape head according to one embodiment.

FIG. 2B is a tape bearing surface view taken from Line 2B of FIG. 2A.

FIG. 2C is a detailed view taken from Circle 2C of FIG. 2B.

FIG. 2D is a detailed view of a partial tape bearing surface of a pairof modules.

FIG. 3 is a partial tape bearing surface view of a magnetic head havinga write-read-write configuration.

FIG. 4 is a partial tape bearing surface view of a magnetic head havinga read-write-read configuration.

FIG. 5 is a side view of a magnetic tape head with three modulesaccording to one embodiment where the modules all generally lie alongabout parallel planes.

FIG. 6 is a side view of a magnetic tape head with three modules in atangent (angled) configuration.

FIG. 7 is a side view of a magnetic tape head with three modules in anoverwrap configuration.

FIGS. 8A-8C are schematics depicting the principles of tape tenting.

FIG. 9 is a representational diagram of files and indexes stored on amagnetic tape according to one embodiment.

FIG. 10A is a top wafer level view of an apparatus according to oneembodiment.

FIG. 10B is a top bearing surface view of an apparatus including shieldsaccording to one embodiment.

FIG. 10C is a detailed view taken from Circle 10C of FIG. 10B.

FIG. 10D is a detailed view taken from Circle 10D of FIG. 10B.

FIG. 11 is a representative view of an apparatus according to oneembodiment.

FIG. 12 is a representative view of an apparatus according to oneembodiment.

FIG. 13A is a bearing surface view of an apparatus according to oneembodiment.

FIG. 13B is a bearing surface view of an apparatus according to oneembodiment

FIG. 13C is a bearing surface view of an apparatus according to oneembodiment.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating thegeneral principles of the present invention and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified.

The following description discloses several preferred embodiments ofmagnetic storage systems, as well as operation and/or component partsthereof.

In one general embodiment, an apparatus includes a plurality of firstcircuits, each first circuit comprising a pair of terminals coupled to afirst read transducer and a first parallel circuit, each first readtransducer having a tunnel valve structure having a resistance. Aterminal resistance of each first circuit is less than the resistance ofthe first read transducer thereof. A second circuit has a pair ofterminals that are coupled to a second read transducer having a tunnelvalve structure. An area of a tunnel barrier portion of the second readtransducer along a plane of deposition thereof is larger than an area ofa tunnel barrier portion of each of the first read transducers along aplane of deposition thereof. A resistivity of a tunnel barrier of eachof the first read transducers is about the same as a resistivity of atunnel barrier layer of the second read transducer. The terminalresistance of each first circuit is less than about five times aterminal resistance of the second circuit.

In another general embodiment, an apparatus includes a module having anarray of first read transducers and a second read transducer, the firstand second read transducers each having a tunnel valve structure. Anarea of a tunnel barrier portion of the second read transducer along aplane of deposition thereof is larger than an area of a tunnel barrierportion of each of the first read transducers along a plane ofdeposition thereof. A parallel circuit is coupled to each of the firstread transducers. A cable couples the first and second read transducersto a controller, thereby forming a plurality of circuits extending fromthe controller, each circuit corresponding to one of the readtransducers. A terminal resistance of each circuit corresponding to thefirst read transducers is less than about five times a terminalresistance of the circuit corresponding to the second read transducer.

Any of these embodiments may be implemented in a magnetic data storagesystem such as a tape drive system, which may include a magnetic head, adrive mechanism for passing a magnetic medium (e.g., recording tape)over the magnetic head, and a controller electrically coupled to themagnetic head.

FIG. 1A illustrates a simplified tape drive 100 of a tape-based datastorage system, which may be employed in the context of the presentinvention. While one specific implementation of a tape drive is shown inFIG. 1A, it should be noted that the embodiments described herein may beimplemented in the context of any type of tape drive system.

As shown, a tape supply cartridge 120 and a take-up reel 121 areprovided to support a tape 122. One or more of the reels may form partof a removable cartridge and are not necessarily part of the system 100.The tape drive, such as that illustrated in FIG. 1A, may further includedrive motor(s) to drive the tape supply cartridge 120 and the take-upreel 121 to move the tape 122 over a tape head 126 of any type. Suchhead may include an array of readers, writers, or both.

Guides 125 guide the tape 122 across the tape head 126. Such tape head126 is in turn coupled to a controller 128 via a cable 130. Thecontroller 128 may be or include a processor and/or any logic forcontrolling any subsystem of the drive 100. For example, the controller128 typically controls head functions such as servo following, datawriting, data reading, etc. The controller 128 may include at least oneservo channel and at least one data channel, each of which include dataflow processing logic configured to process and/or store information tobe written to and/or read from the tape 122. The controller 128 mayoperate under logic known in the art, as well as any logic disclosedherein, and thus may be considered as a processor for any of thedescriptions of tape drives included herein, in various embodiments. Thecontroller 128 may be coupled to a memory 136 of any known type, whichmay store instructions executable by the controller 128. Moreover, thecontroller 128 may be configured and/or programmable to perform orcontrol some or all of the methodology presented herein. Thus, thecontroller 128 may be considered to be configured to perform variousoperations by way of logic programmed into one or more chips, modules,and/or blocks; software, firmware, and/or other instructions beingavailable to one or more processors; etc., and combinations thereof.

The cable 130 may include read/write circuits to transmit data to thehead 126 to be recorded on the tape 122 and to receive data read by thehead 126 from the tape 122. An actuator 132 controls position of thehead 126 relative to the tape 122.

An interface 134 may also be provided for communication between the tapedrive 100 and a host (internal or external) to send and receive the dataand for controlling the operation of the tape drive 100 andcommunicating the status of the tape drive 100 to the host, all as willbe understood by those of skill in the art.

FIG. 1B illustrates an exemplary tape cartridge 150 according to oneembodiment. Such tape cartridge 150 may be used with a system such asthat shown in FIG. 1A. As shown, the tape cartridge 150 includes ahousing 152, a tape 122 in the housing 152, and a nonvolatile memory 156coupled to the housing 152. In some approaches, the nonvolatile memory156 may be embedded inside the housing 152, as shown in FIG. 1B. In moreapproaches, the nonvolatile memory 156 may be attached to the inside oroutside of the housing 152 without modification of the housing 152. Forexample, the nonvolatile memory may be embedded in a self-adhesive label154. In one preferred embodiment, the nonvolatile memory 156 may be aFlash memory device, ROM device, etc., embedded into or coupled to theinside or outside of the tape cartridge 150. The nonvolatile memory isaccessible by the tape drive and the tape operating software (the driversoftware), and/or another device.

By way of example, FIG. 2A illustrates a side view of a flat-lapped,bi-directional, two-module magnetic tape head 200 which may beimplemented in the context of the present invention. As shown, the headincludes a pair of bases 202, each equipped with a module 204, and fixedat a small angle α with respect to each other. The bases may be“U-beams” that are adhesively coupled together. Each module 204 includesa substrate 204A and a closure 204B with a thin film portion, commonlyreferred to as a “gap” in which the readers and/or writers 206 areformed. In use, a tape 208 is moved over the modules 204 along a media(tape) bearing surface 209 in the manner shown for reading and writingdata on the tape 208 using the readers and writers. The wrap angle θ ofthe tape 208 at edges going onto and exiting the flat media supportsurfaces 209 are usually between about 0.1 degree and about 3 degrees.

The substrates 204A are typically constructed of a wear resistantmaterial, such as a ceramic. The closures 204B may be made of the sameor similar ceramic as the substrates 204A.

The readers and writers may be arranged in a piggyback or mergedconfiguration. An illustrative piggybacked configuration comprises a(magnetically inductive) writer transducer on top of (or below) a(magnetically shielded) reader transducer (e.g., a magnetoresistivereader, etc.), wherein the poles of the writer and the shields of thereader are generally separated. An illustrative merged configurationcomprises one reader shield in the same physical layer as one writerpole (hence, “merged”). The readers and writers may also be arranged inan interleaved configuration. Alternatively, each array of channels maybe readers or writers only. Any of these arrays may contain one or moreservo track readers for reading servo data on the medium.

FIG. 2B illustrates the tape bearing surface 209 of one of the modules204 taken from Line 2B of FIG. 2A. A representative tape 208 is shown indashed lines. The module 204 is preferably long enough to be able tosupport the tape as the head steps between data bands.

In this example, the tape 208 includes 4 to 32 data bands, e.g., with 16data bands and 17 servo tracks 210, as shown in FIG. 2B on a one-halfinch wide tape 208. The data bands are defined between servo tracks 210.Each data band may include a number of data tracks, for example 1024data tracks (not shown). During read/write operations, the readersand/or writers 206 are positioned to specific track positions within oneof the data bands. Outer readers, sometimes called servo readers, readthe servo tracks 210. The servo signals are in turn used to keep thereaders and/or writers 206 aligned with a particular set of tracksduring the read/write operations.

FIG. 2C depicts a plurality of readers and/or writers 206 formed in agap 218 on the module 204 in Circle 2B of FIG. 2B. As shown, the arrayof readers and writers 206 includes, for example, 16 writers 214, 16readers 216 and two servo readers 212, though the number of elements mayvary. Illustrative embodiments include 8, 16, 32, 40, and 64 activereaders and/or writers 206 per array, and alternatively interleaveddesigns having odd numbers of reader or writers such as 17, 25, 33, etc.An illustrative embodiment includes 32 readers per array and/or 32writers per array, where the actual number of transducer elements couldbe greater, e.g., 33, 34, etc. This allows the tape to travel moreslowly, thereby reducing speed-induced tracking and mechanicaldifficulties and/or execute fewer “wraps” to fill or read the tape.While the readers and writers may be arranged in a piggybackconfiguration as shown in FIG. 2C, the readers 216 and writers 214 mayalso be arranged in an interleaved configuration. Alternatively, eacharray of readers and/or writers 206 may be readers or writers only, andthe arrays may contain one or more servo readers 212. As noted byconsidering FIGS. 2A and 2B-2C together, each module 204 may include acomplementary set of readers and/or writers 206 for such things asbi-directional reading and writing, read-while-write capability,backward compatibility, etc.

FIG. 2D shows a partial tape bearing surface view of complementarymodules of a magnetic tape head 200 according to one embodiment. In thisembodiment, each module has a plurality of read/write (R/W) pairs in apiggyback configuration formed on a common substrate 204A and anoptional electrically insulative layer 236. The writers, exemplified bythe write transducer 214 and the readers, exemplified by the readtransducer 216, are aligned parallel to an intended direction of travelof a tape medium thereacross to form an R/W pair, exemplified by the R/Wpair 222. Note that the intended direction of tape travel is sometimesreferred to herein as the direction of tape travel, and such terms maybe used interchangeably. Such direction of tape travel may be inferredfrom the design of the system, e.g., by examining the guides; observingthe actual direction of tape travel relative to the reference point;etc. Moreover, in a system operable for bi-direction reading and/orwriting, the direction of tape travel in both directions is typicallyparallel and thus both directions may be considered equivalent to eachother.

Several R/W pairs 222 may be present, such as 8, 16, 32 pairs, etc. TheR/W pairs 222 as shown are linearly aligned in a direction generallyperpendicular to a direction of tape travel thereacross. However, thepairs may also be aligned diagonally, etc. Servo readers 212 arepositioned on the outside of the array of R/W pairs, the function ofwhich is well known.

Generally, the magnetic tape medium moves in either a forward or reversedirection as indicated by arrow 220. The magnetic tape medium and headassembly 200 operate in a transducing relationship in the mannerwell-known in the art. The piggybacked MR head assembly 200 includes twothin-film modules 224 and 226 of generally identical construction.

Modules 224 and 226 are joined together with a space present betweenclosures 204B thereof (partially shown) to form a single physical unitto provide read-while-write capability by activating the writer of theleading module and reader of the trailing module aligned with the writerof the leading module parallel to the direction of tape travel relativethereto. When a module 224, 226 of a piggyback head 200 is constructed,layers are formed in the gap 218 created above an electricallyconductive substrate 204A (partially shown), e.g., of AlTiC, ingenerally the following order for the R/W pairs 222: an insulating layer236, a first shield 232 typically of an iron alloy such as NiFe (−),cobalt zirconium tantalum (CZT) or Al—Fe—Si (Sendust), a sensor 234 forsensing a data track on a magnetic medium, a second shield 238 typicallyof a nickel-iron alloy (e.g., ˜80/20 at % NiFe, also known aspermalloy), first and second writer pole tips 228, 230, and a coil (notshown). The sensor may be of any known type, including those based onMR, GMR, AMR, tunneling magnetoresistance (referred to as tunnel valveand TMR), etc.

The first and second writer poles 228, 230 may be fabricated from highmagnetic moment materials such as ˜45/55 NiFe. Note that these materialsare provided by way of example only, and other materials may be used.Additional layers such as insulation between the shields and/or poletips and an insulation layer surrounding the sensor may be present.Illustrative materials for the insulation include alumina and otheroxides, insulative polymers, etc.

The configuration of the tape head 126 according to one embodimentincludes multiple modules, preferably three or more. In awrite-read-write (W-R-W) head, outer modules for writing flank one ormore inner modules for reading. Referring to FIG. 3, depicting a W-R-Wconfiguration, the outer modules 252, 256 each include one or morearrays of writers 260. The inner module 254 of FIG. 3 includes one ormore arrays of readers 258 in a similar configuration. Variations of amulti-module head include a R-W-R head (FIG. 4), a R-R-W head, a W-W-Rhead, etc. In yet other variations, one or more of the modules may haveread/write pairs of transducers. Moreover, more than three modules maybe present. In further approaches, two outer modules may flank two ormore inner modules, e.g., in a W-R-R-W, a R-W-W-R arrangement, etc. Forsimplicity, a W-R-W head is used primarily herein to exemplifyembodiments of the present invention. One skilled in the art apprisedwith the teachings herein will appreciate how permutations of thepresent invention would apply to configurations other than a W-R-Wconfiguration.

FIG. 5 illustrates a magnetic head 126 according to one embodiment ofthe present invention that includes first, second and third modules 302,304, 306 each having a tape bearing surface 308, 310, 312 respectively,which may be flat, contoured, etc. Note that while the term “tapebearing surface” appears to imply that the surface facing the tape 315is in physical contact with the tape bearing surface, this is notnecessarily the case. Rather, only a portion of the tape may be incontact with the tape bearing surface, constantly or intermittently,with other portions of the tape riding (or “flying”) above the tapebearing surface on a layer of air, sometimes referred to as an “airbearing”. The first module 302 will be referred to as the “leading”module as it is the first module encountered by the tape in a threemodule design for tape moving in the indicated direction. The thirdmodule 306 will be referred to as the “trailing” module. The trailingmodule follows the middle module and is the last module seen by the tapein a three module design. The leading and trailing modules 302, 306 arereferred to collectively as outer modules. Also, note that the outermodules 302, 306 will alternate as leading modules, depending on thedirection of travel of the tape 315.

In one embodiment, the tape bearing surfaces 308, 310, 312 of the first,second and third modules 302, 304, 306 lie on about parallel planes(which is meant to include parallel and nearly parallel planes, e.g.,between parallel and tangential as in FIG. 6), and the tape bearingsurface 310 of the second module 304 is above the tape bearing surfaces308, 312 of the first and third modules 302, 306. As described below,this has the effect of creating the desired wrap angle α₂ of the taperelative to the tape bearing surface 310 of the second module 304.

Where the tape bearing surfaces 308, 310, 312 lie along parallel ornearly parallel yet offset planes, intuitively, the tape should peel offof the tape bearing surface 308 of the leading module 302. However, thevacuum created by the skiving edge 318 of the leading module 302 hasbeen found by experimentation to be sufficient to keep the tape adheredto the tape bearing surface 308 of the leading module 302. The trailingedge 320 of the leading module 302 (the end from which the tape leavesthe leading module 302) is the approximate reference point which definesthe wrap angle α₂ over the tape bearing surface 310 of the second module304. The tape stays in close proximity to the tape bearing surface untilclose to the trailing edge 320 of the leading module 302. Accordingly,read and/or write elements 322 may be located near the trailing edges ofthe outer modules 302, 306. These embodiments are particularly adaptedfor write-read-write applications.

A benefit of this and other embodiments described herein is that,because the outer modules 302, 306 are fixed at a determined offset fromthe second module 304, the inner wrap angle α₂ is fixed when the modules302, 304, 306 are coupled together or are otherwise fixed into a head.The inner wrap angle α₂ is approximately tan⁻¹(δ/W) where δ is theheight difference between the planes of the tape bearing surfaces 308,310 and W is the width between the opposing ends of the tape bearingsurfaces 308, 310. An illustrative inner wrap angle α₂ is in a range ofabout 0.3° to about 1.1°, though can be any angle required by thedesign.

Beneficially, the inner wrap angle α₂ on the side of the module 304receiving the tape (leading edge) will be larger than the inner wrapangle α₃ on the trailing edge, as the tape 315 rides above the trailingmodule 306. This difference is generally beneficial as a smaller α₃tends to oppose what has heretofore been a steeper exiting effectivewrap angle.

Note that the tape bearing surfaces 308, 312 of the outer modules 302,306 are positioned to achieve a negative wrap angle at the trailing edge320 of the leading module 302. This is generally beneficial in helpingto reduce friction due to contact with the trailing edge 320, providedthat proper consideration is given to the location of the crowbar regionthat forms in the tape where it peels off the head. This negative wrapangle also reduces flutter and scrubbing damage to the elements on theleading module 302. Further, at the trailing module 306, the tape 315flies over the tape bearing surface 312 so there is virtually no wear onthe elements when tape is moving in this direction. Particularly, thetape 315 entrains air and so will not significantly ride on the tapebearing surface 312 of the third module 306 (some contact may occur).This is permissible, because the leading module 302 is writing while thetrailing module 306 is idle.

Writing and reading functions are performed by different modules at anygiven time. In one embodiment, the second module 304 includes aplurality of data and optional servo readers 331 and no writers. Thefirst and third modules 302, 306 include a plurality of writers 322 andno data readers, with the exception that the outer modules 302, 306 mayinclude optional servo readers. The servo readers may be used toposition the head during reading and/or writing operations. The servoreader(s) on each module are typically located towards the end of thearray of readers or writers.

By having only readers or side by side writers and servo readers in thegap between the substrate and closure, the gap length can besubstantially reduced. Typical heads have piggybacked readers andwriters, where the writer is formed above each reader. A typical gap is20-35 microns. However, irregularities on the tape may tend to droopinto the gap and create gap erosion. Thus, the smaller the gap is thebetter. The smaller gap enabled herein exhibits fewer wear relatedproblems.

In some embodiments, the second module 304 has a closure, while thefirst and third modules 302, 306 do not have a closure. Where there isno closure, preferably a hard coating is added to the module. Onepreferred coating is diamond-like carbon (DLC).

In the embodiment shown in FIG. 5, the first, second, and third modules302, 304, 306 each have a closure 332, 334, 336, which extends the tapebearing surface of the associated module, thereby effectivelypositioning the read/write elements away from the edge of the tapebearing surface. The closure 332 on the second module 304 can be aceramic closure of a type typically found on tape heads. The closures334, 336 of the first and third modules 302, 306, however, may beshorter than the closure 332 of the second module 304 as measuredparallel to a direction of tape travel over the respective module. Thisenables positioning the modules closer together. One way to produceshorter closures 334, 336 is to lap the standard ceramic closures of thesecond module 304 an additional amount. Another way is to plate ordeposit thin film closures above the elements during thin filmprocessing. For example, a thin film closure of a hard material such asSendust or nickel-iron alloy (e.g., 45/55) can be formed on the module.

With reduced-thickness ceramic or thin film closures 334, 336 or noclosures on the outer modules 302, 306, the write-to-read gap spacingcan be reduced to less than about 1 mm, e.g., about 0.75 mm, or 50% lessthan commonly-used Linear Tape Open (LTO) tape head spacing. The openspace between the modules 302, 304, 306 can still be set toapproximately 0.5 to 0.6 mm, which in some embodiments is ideal forstabilizing tape motion over the second module 304.

Depending on tape tension and stiffness, it may be desirable to anglethe tape bearing surfaces of the outer modules relative to the tapebearing surface of the second module. FIG. 6 illustrates an embodimentwhere the modules 302, 304, 306 are in a tangent or nearly tangent(angled) configuration. Particularly, the tape bearing surfaces of theouter modules 302, 306 are about parallel to the tape at the desiredwrap angle α₂ of the second module 304. In other words, the planes ofthe tape bearing surfaces 308, 312 of the outer modules 302, 306 areoriented at about the desired wrap angle α₂ of the tape 315 relative tothe second module 304. The tape will also pop off of the trailing module306 in this embodiment, thereby reducing wear on the elements in thetrailing module 306. These embodiments are particularly useful forwrite-read-write applications. Additional aspects of these embodimentsare similar to those given above.

Typically, the tape wrap angles may be set about midway between theembodiments shown in FIGS. 5 and 6.

FIG. 7 illustrates an embodiment where the modules 302, 304, 306 are inan overwrap configuration. Particularly, the tape bearing surfaces 308,312 of the outer modules 302, 306 are angled slightly more than the tape315 when set at the desired wrap angle α₂ relative to the second module304. In this embodiment, the tape does not pop off of the trailingmodule, allowing it to be used for writing or reading. Accordingly, theleading and middle modules can both perform reading and/or writingfunctions while the trailing module can read any just-written data.Thus, these embodiments are preferred for write-read-write,read-write-read, and write-write-read applications. In the latterembodiments, closures should be wider than the tape canopies forensuring read capability. The wider closures may require a widergap-to-gap separation. Therefore, a preferred embodiment has awrite-read-write configuration, which may use shortened closures thatthus allow closer gap-to-gap separation.

Additional aspects of the embodiments shown in FIGS. 6 and 7 are similarto those given above.

A 32 channel version of a multi-module head 126 may use cables 350having leads on the same or smaller pitch as current 16 channelpiggyback LTO modules, or alternatively the connections on the modulemay be organ-keyboarded for a 50% reduction in cable span. Over-under,writing pair unshielded cables may be used for the writers, which mayhave integrated servo readers.

The outer wrap angles α₁ may be set in the drive, such as by guides ofany type known in the art, such as adjustable rollers, slides, etc. oralternatively by outriggers, which are integral to the head. Forexample, rollers having an offset axis may be used to set the wrapangles. The offset axis creates an orbital arc of rotation, allowingprecise alignment of the wrap angle α₁.

To assemble any of the embodiments described above, conventional u-beamassembly can be used. Accordingly, the mass of the resultant head may bemaintained or even reduced relative to heads of previous generations. Inother approaches, the modules may be constructed as a unitary body.Those skilled in the art, armed with the present teachings, willappreciate that other known methods of manufacturing such heads may beadapted for use in constructing such heads. Moreover, unless otherwisespecified, processes and materials of types known in the art may beadapted for use in various embodiments in conformance with the teachingsherein, as would become apparent to one skilled in the art upon readingthe present disclosure.

As a tape is run over a module, it is preferred that the tape passessufficiently close to magnetic transducers on the module such thatreading and/or writing is efficiently performed, e.g., with a low errorrate. According to some approaches, tape tenting may be used to ensurethe tape passes sufficiently close to the portion of the module havingthe magnetic transducers. To better understand this process, FIGS. 8A-8Cillustrate the principles of tape tenting. FIG. 8A shows a module 800having an upper tape bearing surface 802 extending between oppositeedges 804, 806. A stationary tape 808 is shown wrapping around the edges804, 806. As shown, the bending stiffness of the tape 808 lifts the tapeoff of the tape bearing surface 802. Tape tension tends to flatten thetape profile, as shown in FIG. 8A. Where tape tension is minimal, thecurvature of the tape is more parabolic than shown.

FIG. 8B depicts the tape 808 in motion. The leading edge, i.e., thefirst edge the tape encounters when moving, may serve to skive air fromthe tape, thereby creating a subambient air pressure between the tape808 and the tape bearing surface 802. In FIG. 8B, the leading edge isthe left edge and the right edge is the trailing edge when the tape ismoving left to right. As a result, atmospheric pressure above the tapeurges the tape toward the tape bearing surface 802, thereby creatingtape tenting proximate each of the edges. The tape bending stiffnessresists the effect of the atmospheric pressure, thereby causing the tapetenting proximate both the leading and trailing edges. Modeling predictsthat the two tents are very similar in shape.

FIG. 8C depicts how the subambient pressure urges the tape 808 towardthe tape bearing surface 802 even when a trailing guide 810 ispositioned above the plane of the tape bearing surface.

It follows that tape tenting may be used to direct the path of a tape asit passes over a module. As previously mentioned, tape tenting may beused to ensure the tape passes sufficiently close to the portion of themodule having the magnetic transducers, preferably such that readingand/or writing is efficiently performed, e.g., with a low error rate.

Magnetic tapes may be stored in tape cartridges that are, in turn,stored at storage slots or the like inside a data storage library. Thetape cartridges may be stored in the library such that they areaccessible for physical retrieval. In addition to magnetic tapes andtape cartridges, data storage libraries may include data storage drivesthat store data to, and/or retrieve data from, the magnetic tapes.Moreover, tape libraries and the components included therein mayimplement a file system which enables access to tape and data stored onthe tape.

File systems may be used to control how data is stored in, and retrievedfrom, memory. Thus, a file system may include the processes and datastructures that an operating system uses to keep track of files inmemory, e.g., the way the files are organized in memory. Linear TapeFile System (LTFS) is an exemplary format of a file system that may beimplemented in a given library in order to enables access to complianttapes. It should be appreciated that various embodiments herein can beimplemented with a wide range of file system formats, including forexample IBM Spectrum Archive Library Edition (LTFS LE). However, toprovide a context, and solely to assist the reader, some of theembodiments below may be described with reference to LTFS which is atype of file system format. This has been done by way of example only,and should not be deemed limiting on the invention defined in theclaims.

A tape cartridge may be “loaded” by inserting the cartridge into thetape drive, and the tape cartridge may be “unloaded” by removing thetape cartridge from the tape drive. Once loaded in a tape drive, thetape in the cartridge may be “threaded” through the drive by physicallypulling the tape (the magnetic recording portion) from the tapecartridge, and passing it above a magnetic head of a tape drive.Furthermore, the tape may be attached on a take-up reel (e.g., see 121of FIG. 1A above) to move the tape over the magnetic head.

Once threaded in the tape drive, the tape in the cartridge may be“mounted” by reading metadata on a tape and bringing the tape into astate where the LTFS is able to use the tape as a constituent componentof a file system. Moreover, in order to “unmount” a tape, metadata ispreferably first written on the tape (e.g., as an index), after whichthe tape may be removed from the state where the LTFS is allowed to usethe tape as a constituent component of a file system. Finally, to“unthread” the tape, the tape is unattached from the take-up reel and isphysically placed back into the inside of a tape cartridge again. Thecartridge may remain loaded in the tape drive even after the tape hasbeen unthreaded, e.g., waiting for another read and/or write request.However, in other instances, the tape cartridge may be unloaded from thetape drive upon the tape being unthreaded, e.g., as described above.

Magnetic tape is a sequential access medium. Thus, new data is writtento the tape by appending the data at the end of previously written data.It follows that when data is recorded in a tape having only onepartition, metadata (e.g., allocation information) is continuouslyappended to an end of the previously written data as it frequentlyupdates and is accordingly rewritten to tape. As a result, the rearmostinformation is read when a tape is first mounted in order to access themost recent copy of the metadata corresponding to the tape. However,this introduces a considerable amount of delay in the process ofmounting a given tape.

To overcome this delay caused by single partition tape mediums, the LTFSformat includes a tape that is divided into two partitions, whichinclude an index partition and a data partition. The index partition maybe configured to record metadata (meta information), e.g., such as fileallocation information (Index), while the data partition may beconfigured to record the body of the data, e.g., the data itself.

Looking to FIG. 9, a magnetic tape 900 having an index partition 902 anda data partition 904 is illustrated according to one embodiment. Asshown, data files and indexes are stored on the tape. The LTFS formatallows for index information to be recorded in the index partition 902at the beginning of tape 906, as would be appreciated by one skilled inthe art upon reading the present description.

As index information is updated, it preferably overwrites the previousversion of the index information, thereby allowing the currently updatedindex information to be accessible at the beginning of tape in the indexpartition. According to the specific example illustrated in FIG. 9, amost recent version of metadata Index 3 is recorded in the indexpartition 902 at the beginning of the tape 906. Conversely, all threeversion of metadata Index 1, Index 2, Index 3 as well as data File A,File B, File C, File D are recorded in the data partition 904 of thetape. Although Index 1 and Index 2 are old (e.g., outdated) indexes,because information is written to tape by appending it to the end of thepreviously written data as described above, these old indexes Index 1,Index 2 remain stored on the tape 900 in the data partition 904 withoutbeing overwritten.

The metadata may be updated in the index partition 902 and/or the datapartition 904 differently depending on the desired embodiment. Accordingto some embodiments, the metadata of the index partition 902 may beupdated in response to the tape being unmounted, e.g., such that theindex may be read from the index partition when that tape is mountedagain. The metadata may also be written in the data partition 902 so thetape may be mounted using the metadata recorded in the data partition902, e.g., as a backup option.

According to one example, which is no way intended to limit theinvention, LTFS LE may be used to provide the functionality of writingan index in the data partition when a user explicitly instructs thesystem to do so, or at a time designated by a predetermined period whichmay be set by the user, e.g., such that data loss in the event of suddenpower stoppage can be mitigated.

As data density increases, track widths are reduced to accommodate moretracks per tape for more data. Thus, the data readers become smaller tofit the decreasing widths of the tracks. However, in conventional taperecording heads, servo track readers (see FIGS. 2A-2C) tend to have alarger size for reading servo data on the medium. The size of the servotrack readers has changed very little from generation to generation ofmedium. For example, the dimensions of the servo pattern of the standardLTO-compliant tape has had minimal changes since the first generation ofLTO in the year 2000 to the 7^(th) generation (in 2015).

Conventional methods to build the tunnel valve sensors involve blanketdepositions to create these tunnel valve structures, and the depositionsare common (i.e., the same) for both data and servo elements. Thus, thedata and servo elements may be built concurrently with the samematerials and processes. With increasing numbers of tracks, because thetrack widths are reduced, the data reader dimensions are also reduced.For efficient data reading, the reader widths are adjusted according totrack width. When data reader dimensions are reduced to enable readingsmaller track widths that are required for high density recording,tunnel barrier resistivity may also be reduced to preserve data readerresistances.

Tunnel barrier resistivity may be calculated according to Equation 1.R=RA/(w×h)  Equation 1

-   -   The tunnel valve sensor resistance R is equal to the RA of the        tunnel valve barrier divided by the product of the sensor        height (h) and sensor width (w). RA is the tunnel barrier        resistivity in ohms·area (Ωμm²)

For example, if a data sensor has an RA of 4 Ωμm² and sensor dimensionsof w=0.2 μm, h=0.2 μm, then the data sensor resistance (R)=100Ω. On theother hand, servo readers may have w=2 μm and h=0.6 μm with R=3.3Ω. ButR may preferably be 30-80Ω in some embodiments. Thus, RA for servoreaders would need to be about 40-60 Ωμm².

Servo reader dimensions have historically remained constant.Conventional servo readers are constrained to have widths in the 2 μmrange to accommodate position error signaling issues and backwardcompatibility with earlier generation of products. Thus, in conventionalheads, a RA of 4 Ωμm², but with servo reader dimensions of w=2.0 μm,h=0.6 μm, the servo resistance (R) would be 3.3Ω, and thus, too low forsignal processing of the servo signal.

There are no known solutions to this problem for servo readers in amultichannel reading module having tunnel valve transducers.

Various embodiments described herein include using the same material, ormaterial with similar RA values, for the tunnel barrier layers of boththe data sensors and the servo sensors. In some approaches, this allowsthe servo reader resistance to remain about the same from generation togeneration while the resistance in the data reader circuits may beincreased, thereby enabling narrower reader width heads havingacceptable resistance values.

One embodiment of an apparatus includes a first read transducer having atunnel valve structure, and a second read transducer having a tunnelvalve structure. Furthermore, the tunnel valve structure of the firstread transducer has about the same resistivity (within 10%) as thetunnel valve structure of the second read transducer.

FIGS. 10A-10D depict an apparatus 1000 of a magnetic recording modulehaving tunnel valve sensors with similar tunnel barrier resistivities,in accordance with one embodiment. As an option, the present apparatus1000 may be implemented in conjunction with features from any otherembodiment listed herein, such as those described with reference to theother FIGS. Of course, however, such an apparatus 1000 and otherspresented herein may be used in various applications and/or inpermutations which may or may not be specifically described in theillustrative embodiments listed herein. Further, the apparatus 1000presented herein may be used in any desired environment.

FIG. 10A shows a wafer level view of an embodiment of apparatus 1000.

According to one embodiment, the first read transducer 1012 has a tunnelvalve structure 1006 and a second read transducer 1010 has a tunnelvalve structure 1004. For example, the first read transducers may bedata readers, while the second read transducers may be servo readers,e.g., as shown in FIG. 10A. However, as noted below e.g., with referenceto FIGS. 13A-13C, the first and second read transducers may be presentin various combinations of data readers only, data readers and servoreaders, etc.

In one embodiment of apparatus 1000, the read transducers 1010, 1012, inan array 1001, etc. may be in a magnetic tape head. Furthermore, in someapproaches, apparatus 1000 includes a drive mechanism for passing amagnetic medium over the read transducers (e.g., as illustrated in FIG.1A); and a controller (e.g., 128 in FIG. 1A) electrically coupled to theread transducers.

FIG. 10B shows a tape bearing surface view of the apparatus 1000.According to one embodiment, the first read transducer 1012 has a tunnelvalve structure 1006 with a bottom shield 1008, a top shield 1009, andelectrically conductive spacer layers 1011 between each shield and theassociated read transducer. Looking to the magnified view (Circle 10D)of the tunnel valve structure 1006 in FIG. 10D, the tunnel valvestructure 1006 may have an antiferromagnetic layer 1014, a referencelayer 1016 (such as a synthetic pinned layer structure havingantiparallel-pinned layers), a tunnel barrier layer 1024, a free layer1020, and a sensor cap 1022. In some approaches, the tunnel valvestructure 1006 may have more thin film layers. In other approaches, thetunnel valve structure 1006 may have less thin film layers.

According to one embodiment of apparatus 1000, the tunnel valvestructure 1006 may include basically anything between the spacer layers1011 which provide a non-magnetic electrical connection to the shields,and excluding layers along the side edges of the trimmed sensor stack(e.g., excluding hard bias layers 1002 and insulating layers 1026, asshown in FIGS. 10C and 10D, etc.).

According to one embodiment of apparatus 1000, a second read transducer1010 may be on the same module as the first read transducer 1012, thesecond read transducer 1010 having a tunnel valve structure 1004, wherethe tunnel valve structure 1006 of the first read transducer 1012 hasabout the same resistivity as the tunnel valve structure 1004 of thesecond read transducer 1010. A slight difference in resistivity may bepresent due to process variations, even though the tunnel barrier layersare formed concurrently in the same processing step. Conventionalmaterials may be used to fabricate the tunnel barrier layers, such asmagnesium oxide.

Looking to a magnified view (Circle 10C) of the tunnel valve structure1004 of the second read transducer 1010, as shown in FIG. 10C, thetunnel valve structure 1004 may have an antiferromagnetic layer 1014, areference layer 1016 (including a synthetic pinned layer structurehaving antiparallel-pinned layers), a tunnel barrier layer 1018, a freelayer 1020, and a sensor cap 1022. In some approaches, the tunnel valvestructure 1004 may have more thin film layers. In other approaches, thetunnel valve structure 1004 may have less thin film layers.

In various embodiments of apparatus 1000, and as shown in the magnifiedviews of FIGS. 10C and 10D, the tunnel valve structure 1006 of the firstread transducer 1012 may have a tunnel barrier layer 1024 that has aboutthe same resistivity as the tunnel barrier layer 1018 of the tunnelvalve structure 1004 of the second read transducer 1010. However, anarea of the tunnel barrier portion of the second read transducer 1010along a plane of deposition thereof may be larger than an area of thetunnel barrier portion of each of the first read transducers 1012 alonga plane of deposition thereof, such as when the first read transducersare data transducers and the second read transducers are servotransducers. For example, the area of the tunnel barrier portion of thesecond read transducer may be two times the area of the tunnel barrierportion of each first read transducer, or greater. Heights of the tunnelbarrier portions of the each first read transducers 1012 may be aboutthe same as the height of the tunnel barrier portion of the second readtransducer 1010. However, in some approaches, each first read transducer1012 may have a lesser height than the second read transducer 1010.

Due to the relatively different areas of the tunnel barrier layers ofthe first and second read transducers, the overall resistance of thefirst read transducer, e.g., as measured across the upper and lowerleads (e.g., shields) of the first read transducer, is higher than theoverall resistance of the second read transducer when measured in asimilar manner. See Equation 1, above.

Referring to FIG. 11, which depicts an embodiment of apparatus 1000, thefirst read transducers 1012 are each part of a respective first circuit1102, while the second read transducers 1010 are each part of arespective second circuit 1104.

Each first circuit 1102 has a parallel circuit 1106 electrically coupledto the associated first read transducer 1012. A terminal resistance, asmeasured at the terminals 1108 of each first circuit 1102, is less thanthe resistance of the first read transducer 1006 of the respective firstcircuit 1102. In general, a terminal resistance as described herein aremeasured at distal ends of the described circuit, e.g., as measured atpads at the end of the cable positioned farthest from the transducers.

The second circuits 1104 may or may not have a parallel circuitelectrically coupled to the associated second read transducer 1010.Preferably, the second circuits 1104 do not have a parallel circuit. Ifthe second circuit 1104 has a parallel circuit, the resistance of thesecond parallel circuit may be different than a resistance of each ofthe parallel circuits of the first circuits.

The parallel circuits may each include one or more resistors, e.g., ofconventional construction. The various parallel circuits may also and/oralternatively have any other construction using conventional componentsto provide the desired terminal resistance for the circuit.

The resistance value of each parallel circuit 1106 is preferably a valuethat results in the terminal resistance of each first circuit 1102, asmeasured at the terminals 1108 thereof, being less than about five timesthe terminal resistance of the second circuit 1104 as measured atterminals 1108 located at the distal end of the second circuit. Morepreferably, the resistance value of each parallel circuit 1106 is avalue that results in the terminal resistance of each first circuit 1102being less than about two times the terminal resistance of the secondcircuit 1104 as measured at the terminals 1108 of the respectivecircuit. In some approaches, the resistance value of each parallelcircuit 1106 is a value that results in the terminal resistance of eachfirst circuit 1102 being within about 10% of the terminal resistance ofthe second circuit 1104 as measured at the terminals 1108 of therespective circuit. Accordingly, the resistance value of each parallelcircuit may be dependent upon the properties of the various componentsof the apparatus, and thus may be readily calculated using knownformulae and design values for the various components of the apparatus.

In various embodiments, the parallel circuits may be located in therespective circuits at any suitable location.

In one embodiment, the first and second circuits 1102, 1104 includeleads extending from the respective transducer to pads on a module. Thepads may be the terminals in some embodiments. The first and secondcircuits may be integrated in a module. The parallel circuits may beformed when leads are formed. In some approaches, the parallel circuitsmay be external to thin films that are part of the respective transducerstack.

In another embodiment, the parallel circuits are coupled to an exteriorof a module, i.e., the parallel circuits are separate components fromthe module.

The first and second circuits 1102, 1104 may further include leads of acable in electrical communication with the transducers. The terminals atthe distal ends of the first and second circuits 1102, 1104 may be theleads or pads at the end of the cable farthest from the transducers. Forexample, the parallel circuits may be embodied in an interposer locatedat one end of the cable or the other and interposed between the cableand the proximal component. The interposer may be in the form of a chip,circuit board, etc. In another example, the parallel circuits may beembodied in a chip coupled to pads of a module, pads or leads of acable, etc.

In yet another approach, the parallel circuits are coupled directly toleads of a cable, and can be positioned toward either end of the cable.One example is a silicon resistor array coupled to leads or pads of thecable. Preferably, in such approach, the parallel circuits are coupleddirectly to the leads of the cable toward an end of the cable locatedclosest to the read transducers.

In yet another embodiment, the parallel circuits are located on acircuit board to which the cable is attached. For example, the circuitboard may be part of a tape drive controller.

FIG. 12 illustrates an embodiment of the apparatus 1000, where theapparatus 1000 includes a controller 128 and a cable 130 coupling theread transducers 1010, 1012 to the controller 128, thereby forming aplurality of circuits 1102, 1104 corresponding to one of the transducers1010, 1012 and extending from the controller 128. Each circuit hasterminals 1108 electrically coupled to the controller at the distal endsof the respective circuit. A parallel circuit 1206 is also shown in eachsecond circuit 1104. The read transducers 1010, 1012 are embodied in amodule 1208.

Again, the depicted location of the parallel circuits 1106, 1206 isexemplary only. For example, the parallel circuits 1106 and/or 1206 maybe embodied in an interposer positioned between the cable 130 and module1208 and/or between the cable 128 and controller 128; on the circuitboard of the controller 128; etc.

Track widths for data readers may change from generation to generationof tape recording products. Thus, various embodiments described belowallow different data reader widths to accommodate changing track widthsand various formats. Magnetic tape heads may be formed with data readersaligned according to a specification format to read multiple generationsof tapes with different track widths. In addition, new generations mayrequire more channels.

FIGS. 13A-13C depict apparatuses 1300, 1302, 1306 having tunnel valvesensors with similar tunnel barrier resistivities but different areas,in accordance with one embodiment. As an option, present apparatuses1300, 1302, 1306 may be implemented in conjunction with features fromany other embodiment listed herein, such as those described withreference to the other FIGS. Of course, however, such apparatuses 1300,1302, 1306 and others presented herein may be used in variousapplications and/or in permutations which may or may not be specificallydescribed in the illustrative embodiments listed herein. Further, theapparatuses 1300, 1302, 1306 presented herein may be used in any desiredenvironment.

In one embodiment of apparatus 1300 as shown in FIG. 13A, the first readtransducer may be a first data reader 1305 and the second readtransducer may be a second data reader 1307. According to one embodimentof apparatus 1300, a first read transducer 1305 may be on a same moduleas the second read transducer 1307, the second read transducer 1307having a tunnel valve structure, where the tunnel valve structure of thefirst read transducer 1305 has a similar resistivity than the tunnelvalve structure of the second read transducer 1307. In some approaches,as shown in FIG. 13A, the data readers of the array 1301 may be analternating (interleaved) pattern of a second data reader 1307 for onegeneration of tape and a first data reader 1305 for a later generationof tape format. In some approaches, the first and second data readersmay operate together to read a later generation of tape format.

In various embodiments, the width of the tunnel barrier layer of thetunnel valve structure may vary within an array of data readers. Forexample, according to one embodiment of apparatus 1302, FIG. 13Billustrates an array 1303 of data readers with different widths oftunnel barrier layers for each data reader. In some approaches, theresistivity of the tunnel valve structure of the second data reader 1308may have a different width of tunnel barrier layer of the third datareader 1309, and so on with each width different in an array 1303. Inthe example shown, the widths of the data readers progressively decreasefrom the center of the array toward the ends of the array. This may bedone to address track misregistration due to tape dimensionalinstability.

An example of another embodiment of a multiformat apparatus may havemultiple arrays of the data readers and/or servo readers having similarresistivities, for example, in a multi-format head having multiplearrays. As illustrated in FIG. 13C, array 1310 may have data readers1313 of different resistivities than the data readers 1314 in array1312, where, for example, each array is designed for a different tapeformat. In apparatus 1306, the two arrays 1310, 1312 of data readers maybe flanked by servo readers 1304 on either side of the arrays 1310,1312. The servo readers 1304 may have different resistivities from thedata readers 1313, 1314 in the arrays 1310, 1312.

In various embodiments, e.g., any of the foregoing embodiments, thesecond read transducer and another second read transducer may be alignedwith a longitudinal axis of the array.

It will be clear that the various features of the foregoing systemsand/or methodologies may be combined in any way, creating a plurality ofcombinations from the descriptions presented above.

The inventive concepts disclosed herein have been presented by way ofexample to illustrate the myriad features thereof in a plurality ofillustrative scenarios, embodiments, and/or implementations. It shouldbe appreciated that the concepts generally disclosed are to beconsidered as modular, and may be implemented in any combination,permutation, or synthesis thereof. In addition, any modification,alteration, or equivalent of the presently disclosed features,functions, and concepts that would be appreciated by a person havingordinary skill in the art upon reading the instant descriptions shouldalso be considered within the scope of this disclosure.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of an embodiment of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

What is claimed is:
 1. An apparatus, comprising: a plurality of firstcircuits, each first circuit comprising a pair of terminals coupled to afirst read transducer and a first parallel circuit, each first readtransducer having a tunnel valve structure having a resistance, whereina terminal resistance of each first circuit is less than the resistanceof the first read transducer thereof; and a second circuit comprising apair of terminals coupled to a second read transducer having a tunnelvalve structure; wherein an area of a tunnel barrier portion of thesecond read transducer along a plane of deposition thereof is largerthan an area of a tunnel barrier portion of each of the first readtransducers along a plane of deposition thereof, wherein a resistivityof a tunnel barrier of each of the first read transducers is about thesame as a resistivity of a tunnel barrier layer of the second readtransducer, wherein the terminal resistance of each first circuit isless than about five times a terminal resistance of the second circuit.2. An apparatus as recited in claim 1, wherein the first readtransducers are data readers, wherein the second read transducer is aservo reader.
 3. An apparatus as recited in claim 1, wherein the area ofthe tunnel barrier portion of the second read transducer is at least twotimes the area of the tunnel barrier portion of each first readtransducer.
 4. An apparatus as recited in claim 1, wherein each firstread transducer has a greater height than the second read transducer. 5.An apparatus as recited in claim 1, wherein the first read transducersare arranged in an array, wherein the second read transducer is alignedwith a longitudinal axis of the array.
 6. An apparatus as recited inclaim 1, wherein each first read transducer is a first data reader,wherein the second read transducer is a second data reader.
 7. Anapparatus as recited in claim 1, wherein the first and second readtransducers are in a magnetic tape head.
 8. An apparatus as recited inclaim 1, wherein the first parallel circuits are coupled to an exteriorof a module.
 9. An apparatus as recited in claim 1, wherein the firstparallel circuits are coupled directly to leads of a cable.
 10. Anapparatus as recited in claim 9, wherein the first parallel circuits arecoupled directly to the leads of the cable toward an end of the cablelocated closest to the first and second read transducers.
 11. Anapparatus as recited in claim 1, wherein the first and second circuitsare integrated in a module.
 12. An apparatus as recited in claim 1,wherein the first parallel circuits are located on a circuit board towhich a cable is attached.
 13. An apparatus as recited in claim 1,wherein the second circuit comprises a second parallel circuit coupledto the second read transducer, wherein a resistance of the secondparallel circuit is different than a resistance of each of the firstparallel circuits.
 14. An apparatus as recited in claim 1, furthercomprising: a drive mechanism for passing a magnetic medium over thefirst and second read transducers.
 15. An apparatus, comprising: amodule having an array of first read transducers and a second readtransducer, the first and second read transducers each having a tunnelvalve structure, wherein an area of a tunnel barrier portion of thesecond read transducer along a plane of deposition thereof is largerthan an area of a tunnel barrier portion of each of the first readtransducers along a plane of deposition thereof, a parallel circuitcoupled to each of the first read transducers; a controller; and a cablecoupling the first and second read transducers to the controller,thereby forming a plurality of circuits extending from the controller,each circuit corresponding to one of the read transducers, wherein aterminal resistance of each circuit corresponding to the first readtransducers is less than about five times a terminal resistance of thecircuit corresponding to the second read transducer.
 16. An apparatus asrecited in claim 15, wherein a resistivity of a tunnel barrier portionof each of the first read transducers is about the same as a resistivityof a tunnel barrier portion of the second read transducer.
 17. Anapparatus as recited in claim 15, wherein an area of the tunnel barrierportion of the second read transducer is at least two times an area ofthe tunnel barrier portion of each first read transducer.
 18. Anapparatus as recited in claim 15, comprising a second parallel circuitcoupled to the second read transducer, wherein a resistance of thesecond parallel circuit is different than a resistance of each of theparallel circuits coupled to the first read transducers.
 19. Anapparatus as recited in claim 15, wherein the first and second readtransducers are in a magnetic tape head.